Dust mites come from various sources, not only dust. Although not neccissarily dust mites, the most common source we see are birds that have nested in fascias or eaves. The birds can carry mites that will multiply in the nesting site since they have the birds as a consistent food source. When they overpopulate the nest, they will move into the home. The second most common source would be stored garments or bedding. These items are typically stored in closets or attics that are humid and mites love humid environments.